Chemical process



United States Patent Office 3,355,262 CHEMICAL PROCESS Francis M. Beaird, Jr., and Paul Kobetz, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Sept. 30, 1963, Ser. No. 312,281 7 Claims. (Cl. 23-365) ABSTRACT OF THE DISCLOSURE A process for preparing sodium aluminum tetrahydride comprising reacting together sodium aluminum hexahydride, aluminum and hydrogen, the over-all reaction being represented by the equation:

Na AlH +2Al+3H 3NaAlH The reaction is conducted in an inert reaction medium at a temperature ranging from 50 C. to 200 C. at a preferred pressure of from about 1000 to about 5000 pounds per square inch.

Processes of this character are described 2,567,972.

Another major process for the manufacture of sodium aluminum tetrahydride is the Ashby process, described in French Patent 1,235,680. According to this process, sodium, or if desired, sodium hydride, and aluminum metal, preferably in highly subdivided form, are subjected to pressure hydrogenation in a stable reaction medium, the sodium component and the aluminum being in approximately equal molal proportions, although frequently, the aluminum is used in some excess.

The object of the present invention is to provide a process for the manufacture of sodium aluminum tetrahydride. A particular object is to provide a process wherein the reactants include a different component than heretofore used, namely, sodium aluminum hexahydride, Na AlH aluminum, and hydrogen. An object of certain preferred embodiments is to provide a novel two-stage process for obtaining sodium aluminum tetrahydride.

The present process in all forms involves carrying out a reaction between sodium aluminum hexahydride, aluminum metal,and hydrogen, in a mixed phase reaction system, under elevated hydrogen pressure. The reaction accomplished is as follows:

In carrying out the foregoing reaction, a reaction temperature of the order of about 50 to 200 C. is employed, a preferred temperature range being about 100 to 200 C., and an even more preferred range being about 140 to 200 C. with certain media and 100 to 140 C. with certain other reaction media. The components are pro vided, as indicated in the equation, in approximately the proportions of about one mole of sodium aluminum hexahydride, Na AlH and two atoms of aluminum, and the hydrogen 'is consumed in substantially the proportions indicated by the equation.

-As stated, an organic inert liquid reaction medium is provided, generally in the proportions of about 50,,.to

in Patent 3,355,262 Patented Nov. 28, 1967 1000 ml. per gram atom of the sodium content of the sodium aluminum hexahydride, a preferred range being to 500 ml. By inert is meant that the liquid medium is stable or essentially nonreactive with the reactants or product at the reaction conditions used. The liquid reaction media are selected generally from the class of organics consisting of ethers, aliphatic hydrocarbons, and aromatic hydrocarbons, and mixtures thereof. Included in the category of ethers are the simple dialkyl ethers, preferably those having at least three carbon atoms in each alkyl group. More preferred than the simple dialkyl ethers are the lower dialkyl ethers of lower polyethylene glycols, and cyclic ethers, especially tetrahydrofuran. The most preferred temperature range of about to 200 C. is associated with the hydrocarbon reaction media, but the lower preferred range of about 100 to 140 C. is associated with the cyclic ether compounds as certain of these can be cleaved by and will react with the sodium aluminum hydride at temperatures of about 140 C. or above, dependent on the proportions present.

In carrying out the process, an elevated pressure is used, which can be from slightly above one atmosphere up to, for example, about 700 atmospheres, a preferred range of pressures being from about 1000 to 5000 pounds per square inch.

The sodium aluminum hexahydride employed as a re actant is a granular crystalline material, which is insoluble in most of the materials employed as reaction media. Hence, it is surprising that a reaction will occur between this solid material and the aluminum components even though both are solids at the reaction conditions involved.

The aluminum, as already indicated, is preferably in highly subdivided particulate form, in order to provide significant surface and an appreciable reaction rate. The

aluminum is preferably activated by previous treatment. For best results, a catalyst comprising an alkyl compound of aluminum or a similar organometallic material is provided in minor and catalytic proportions, of the order of about 0.1 to 5 volume percent of the liquid reaction medium.

The reaction mixture should be vigorously agitated, and a good degree of completion of reaction will be experienced in a reaction period of 6 to 24 hours.

The mode of carrying out the process will be more readily understood from the following working examples and the further description hereinafter. All proportions are in weight units, except where otherwise specified.

Example 1 A Magne-Dash autoclave was charged with the following components:

Na AlH g 12 Aluminum powder g 6.3 Toluene ml 125 Triethyl aluminum ml 0.6

The aluminum in the foregoing charge was in the proportions of two g. atoms per g. mole of the sodium aluminum hexahydride, the toluene being in proportions of about 350 ml. per gram atom of sodium (1.05 liters per g. mole of the sodium aluminum hexahydride). The aluminum had been previously activated by heating under triethyl aluminum for several hours at 100 C. or over.

The charge was lightly pressurized with hydrogen gas, and the autoclave and contents were heated to C. The hydrogen pressure was raised to 5000 pounds per square inchpressure, and these conditions were maintained while agitating vigorously.

Significant reaction, as shown by a drop in the hydrogen pressure, began after about four hours after initiation of reaction conditions. Following this initiation, hydrogen take-up continued smoothly for eight hours. The autoclave was cooled and analysis of the product showed an 80 percent conversion to sodium aluminum hydride.

4 sodium hydride or sodium, respectively, per atom of the aluminum metal. The reaction carried out can be expressed as The product was provided as very fine gray solids sus- 3Na+Al+3H Na AlH pended in the toluene reaction medium.

Additional examples are summarized in the following It should be understood that variation from these precise table: proportions can be permitted, thus proportions of from Reaction Medium Operating Conditions Catalyst Aluminum to Sodium Alum. Example Hexnliydride Proportion Ml. per

(g. atoms] Material Mljg. atom Temp, Pressure, Reaction Material 100 ml. of g. mole) of Na C. P.s.i.g. Time, Hr. Reaction Medium 2 1.9 Dimethyl ether of diethylene 150 115 6,000 24 'lri-isobutyl 3 glycol. aluminum. 3 2. 3 Diniethyl ether of ethylene 500 180 5,000 Diethyl aluminum 2 glycol. hydride. 4 2.5 Tetrahydroluran 375 140 4,000 Triinetliyl alumi- 5 5 2.1 Methyl ethyl ether oi dietliylerie 400 190 3, 000 18 6 2,05 2,2 gt i methyl pentane 450 210 8,000 6 Trietliyl aluminum 5 7 3.0 100 190 4,000 4 Diisobutylalumi- 1.5

num hydride. 8 2.0 Di-n-hexyl ether 400 160 5,000 10 (None) As indicated in the foregoing examples a variety of about two and one-half to four atoms per atom of alumiconditions can be employed quite efiectively in the num are permissive. The ranges of temperatures and presnumerous embodiments of the process. With certain solsures employed correspond generally to these operating vents having relatively high ethereal oxygen content, such conditions as already stated for the conversion of sodium as the dimethyl ether of diethylene glycol, the sodium aluminum hexahydride to sodium aluminum tetrahydride. aluminum hydride product is in solution in the reaction Upon sufiicient take-up of hydrogen to correspond to a medium. It is preferable in most cases to use a reaction significant yield of sodium aluminum hexahydride, this medium which is not a solvent, such as toluene. In cerstep is discontinued. Usually the pressure is released and tain instances the sodium aluminum hydride can be sucadditional aluminum is provided to correspond to the cessfully crystallized from a rea tio ediu hi h is principal reaction of the process as described above. When a solvent, but in other cases it complexes rather stron ly, desired, the reactor charge from the first stage can be so that isolation as a crystallized product is not feasible. transferred to a Second Stage reactor for this final p Some solvents, particularly tetrahydrofuran, should not tiOh- Generally, it is found that the first Stage, the be subjected to operations at the higher temperatures, conversion of the sodium reactant and aluminum to a owing to its susceptibility to attack by sodium aluminum Composition approximating Sodium aluminum heXatetrahydride if exposed in high concentrations at temperahydride, is at an pp y higher P Tate Teactures above 140 C tion rate than is experienced at comparable conditions The proportions of reaction medium can be greatly for the final Stage of the P v-aried. Generally, liquid media in proportions of about The following example illustrates generally this to 1000 mls. per gram atom of the sodium content of Stage 011158 f m odiments. the sodium aluminum hexahydride is used, a preferred range being 100 to 500 ml. Example 9 As already stated, reaction ressures of from about one atmosphere to about 700 atr iiospheres can be used. A 50 Approxlmately 110 Parts of h dlmethy1.ether of preferred range is 1000 to 5000 pounds per square inch. ethylene glycol 24 Parts by of soduim hydnde Higher pressures tend to shorten the reaction period reand.ab0ut 10 Parts of finely commmuted almpmum metal quired, but mechanical and design problems substantially are f' to the autoclave Th reactor 1s closed and increase above 5000 pounds Pressure. pressured with hydrogen-at an initial pressui'e of about As previously illustrated a catalyst is frequently and 5000 n Square: Inch" A reactlon temperature of profitably used, the preferred catalysts being alkyl alumiabout 140 1s provlded and the hydrogen Pressure num compounds as shown in certain of the examples. dropped. steadl at the rate of about 300 Pound} Per Other catalysts which contain a hydrocarbon radical at- Square mch per hour After sufiiclerit.hydrogen 1S f tached to an active metal can be substituted for the alumisorbed. to corresPond to a 'l Provldmg t p i num compounds specifically illustrated. Thus, sodium i Sodium aluminum hexahydnde the reactlon 1S p ethyl or tetmethyl sodium aluminum can be used in place tmued, and the autoclave and contents cooled to ambient of the catalysts specifically illustrated, and similar results temperature the excess.l.lydrogen Pressure bemg vented will be attained About 20 parts of additional aluminum metal are then A special class of embodiments of the present invention q and reactlon. p l A hlgh ymld of Sodium involves incorporation of the reaction as the second stage alummum.teirahydndeds achieved. of a two-stage process for the manufacture of sodium when f i 0p employmg the reacnon niedla aluminum tetrahydride, NaAlI-l According to such emand Comm/[Ions described m Examples .proylded bodiments, a sodium reactant, either sodium metal or but the reactants Fi charged m the l q sodium hydride, plus subdivided aluminum is pressure followed by addition of further aluminum, similar ultihydrogenated in the presence of a liquid reaction medium mate results are aChIeYedQ stable at reaction conditions and under conditions gensome Instances 1t W111 be issuable to Separate the erally similar to the main process step of the invention sodium aluminum heXa hydride generated in the first stage The sodium reactant is provided in approximately the from the liquid of the reaction medium, and to charge atomic ratio necessary to provide sodium aluminum hexain the Second Stage a different reaction um as Well hydride, viz., preferably about three moles or atoms of 7 as the additional aluminum required.

We claim:

1. The process for making sodium aluminum tetrahydride comprising reacting sodium aluminum hexahydride, aluminum and hydrogen in the presence of an organic liquid reaction medium stable at reaction conditions, said medium being selected from the group consisting of ethers, aliphatic hydrocarbons, andaromatic hydrocarbons and the reaction being at a pressure of about 1000 to 5000 pounds per square inch and at a temperature of about 100 to 200 C.

2. The process of claim 1 further defined in that the liquid reaction medium is an aromatic hydrocarbon, and the pressure is about 1000 to 5000 pounds per square inch.

3. The process of claim 1 further defined in that the liquid reaction medium is an ether, the pressure is about 1 000 to 5000 pounds per square inch and the temperature is about 100 to 140 C.

4. The process of claim 3 further defined in that the liquid reaction medium is tetrahydrofuran.

5. The process of claim 1 further defined in that the liquid reaction medium is the dimethyl ether of diethylene glycol and the pressure is about 1000 to 5000 pounds per square inch.

6. The process for making sodium aluminum tetrahydride comprising reacting sodium aluminum hexahydride, aluminum and hydrogen in the presence of toluene as a liquid react-ion medium, said toluene being in the proportions of 100 to 500 mls. per gram atom of sodium in the sodium aluminum hexahydride, and in the presence of an alkyl aluminum catalyst in the proportions of about 0.1 to 5 volume percent of the toluene, the alumi. num being in the proportions of about two atoms per mole of sodium aluminum hexahydride, the reaction being at a pressure of about 1000 to 5000 pounds per square inch and at a temperature of to 200 C.

7. The process for making sodium aluminum tetrahyd-ride including a first stage comprising reacting a sodium reactant selected from the group consisting of sodium and sodium hydride, subdivided aluminum, and hydrogen, in the presence of an organic liquid reaction medium stable at reaction conditions, said medium being selected from the group consisting of ethers, aliphatic hydrocarbons, and aromatic hydrocarbons, and the reaction being at a pressure of about 1000 to 5000 pounds per square inch and at a temperature of 100 to 200 C., the sodium reactant being in the proportions of about 2 /2 to 4 moles per atom of the aluminum, forming thereby a reaction mixture including sodium aluminum hexahyd-ride, and a second stage comprising adding addition-a1 aluminum to the reaction mixture from the first stage in the proportions of about two atoms per three moles of the original sodium reactant of the first stage, and further reacting with hydrogen and forming thereby sodium aluminum tetrahydride.

Zakharkin et al.: Dokl. Akad. Nauk. SSSR, vol. 145, pp. 793-796, August 1962.

MILTON WEISSMAN, Primary Examiner. OSCAR R. VERTIZ, Examiner. 

1. THE PROCESS FOR MAKING SODIUM ALUMINUM TETRAHYDRIDE COMPRISING REACTIN SODUIUM ALUMINUM HEXAHYDRIDE, ALUMIMUM AND HYDROGEN IN THE PRESENCE OF AN ORGANIC LIQUID REACTION MEDUM STABLE AT REACTION CONDITIONS, SAID MEDIUM BEING SELECTED FROM THE GROUP CONSISTING OF ETHER, ALIPHATIC HYDROCARBONS, AND AROMATIC HYDROCARBONS AND THE REACTION BEING AT A PRESSURE OF ABOUT 1000 TO 5000 POUNDS PER SQUARE INCH AND AT A TEMPERATURE OF ABOUT 100 TO 200*C. 